Known tunable laser sources are, in particular, Bragg reflector (or DBR standing for Distributed Bragg Reflector) lasers in which the adjustment of the emitted wavelength entails a modification of a phase condition of the longitudinal modes of the DBR cavity. This then results in discontinuous tunability with mode jumps. A phase section of the laser source makes it possible to precisely align a resonant mode of the cavity on the desired wavelength. This results in a device which is relatively complex to adjust, in which a control current for the gain section, at least one control current for the distributed reflector or reflectors and a control current for the phase section must be adjusted simultaneously.
In another solution called a Tunable Twin-Guide (TTG) laser, an active layer of InGaAsP material is situated above a passive Bragg grating of InGaAsP material. Independent control currents are injected, on the one hand into the active layer to adjust the gain, and on the other hand into the passive Bragg grating to adjust the wavelength. Given that the Bragg grating, whose effective index can be modified by current injection, is situated directly in the amplification zone, the resonant modes of the DFB (distributed feedback) type are shifted by the very effect of this adjustment without a phase section being necessary. The wavelength tunability is continuous without any jump of modes.